1. Field of the Disclosure
The present disclosure relates generally to electrophotographic image forming devices such as a printer or multifunction device having printing capability, and in particular to a developer unit assembly architecture therefor.
2. Description of the Related Art
Laser printers utilize a light beam which is focused to expose a discrete portion of a photoreceptive or image transfer drum in a further attempt to attract printing toner to these discrete portions. This photoconductive drum assembly is made out of highly photoconductive material that is discharged by light photons typically embodied by a laser. Initially, the drum is given a charge by a charge roller. As the photoreceptive drum revolves, the printer shines a laser beam across the surface to discharge certain points. In this way, the laser “draws” the letters and images to be printed as a pattern of electrical charges—an electrostatic latent image. The system can also work with either a more positively charged electrostatic latent image on more negatively charged background or a more negative charged electrostatic latent image on a more positively charged background.
When the toner becomes electrostatically charged, the toner is attracted to exposed portions of the image transfer roller. After the data image pattern is set, charged toner is supplied to the photoconductive drum. Because of the charge differential between the discharged areas on the photoconductive drum and the charged toner, the toner is attracted to and clings to the discharged areas of the drum, but not to the similarly charged “background” portions of the photoconductive drum. With the toner pattern on the photoconductive drum, the drum engages a sheet of paper or other media moving adjacent thereto. The paper or other media may be driven by a transport belt or transfer roller, which is oppositely charged to the toner causing it to transfer to the paper or other media. This charge is stronger than the charge of the electrostatic image, so the transfer roller pulls the toner away from the surface of the photoconductive drum. When the media passes beneath the rotating photoconductive drum, the toned image is transferred to the media. The transferred toner is subsequently fused to the paper typically by application of heat and pressure.
In order to reduce the premature replacement of components traditionally housed within a toner cartridge for an image forming device, toner cartridge manufacturers have begun to arrange components having a longer life and those having a shorter life into separate replaceable units. Relatively longer life components such as a developer roll, a toner adder roll, a doctor blade and a photoconductive drum are, in some imaging architectures, positioned in one replaceable unit (an “imaging unit”). The image forming device's toner supply, which is consumed relatively quickly in comparison with the components housed in the imaging unit, is provided in a reservoir in a separate replaceable unit in the form of a toner cartridge that mates with the imaging unit within the imaging device. In this configuration, the number of components housed in the toner cartridge is reduced in comparison with traditional toner cartridges. As a result, in systems utilizing a separate toner cartridge and imaging unit, the toner cartridge is often referred to as a “toner bottle” even though the toner cartridge is more complex than a mere bottle for holding toner.
To deliver toner from the toner cartridge to the imaging unit, an auger in the toner cartridge may be used to feed toner from an exit port on the toner cartridge into an entrance port on the imaging unit and in proximity with a second auger that disperses the toner within the imaging unit. A developer roll is a charged rotating roller, typically with a conductive metal shaft and a polymeric conductive coating, which receives toner from a toner adder roll positioned adjacent the developer roll. Due to the electrical charge and mechanical scrubbing, the developer roll collects toner particles from the toner adder roll. A doctor blade assembly engages the developer roll to provide a consistent coating of toner along the length and surface of developer roll, by scraping or “doctoring” excess toner from the developer roll and metering a thin layer of toner on the developer roll surface. In turn, this provides a consistent coating of toner to the photoconductive drum. Without a doctor blade, the coating of toner on the developer roll may be inconsistent, too thick, too thin or bare, thereby causing the amount of toner presented to the latent image of the photoconductive drum to be inconsistent and the level of darkness of the printed image may vary as a result, which is considered a print defect.
One challenge with existing imaging units is that of providing a consistent, cost effective and space saving seal generally around the location where the doctor blade assembly and the imaging unit housing meet due to the tolerances and stiffness of the seal utilized in this location. Accordingly, it would be desirable to inhibit toner leakage in the imaging unit housing without adding additional parts or increasing expense through additional components to seal this area.